To activate clutches in stepped automatic transmissions, pilot valves having downstream hydraulic amplifier elements or actuators are used to vary clutch pressures. The pilot pressure in this case is set, i.e., controlled, via a forward-directed active chain. This principle has two important disadvantages: It is not possible to adequately compensate either the time variance of the controlled system, due to changes in the ambient conditions (such as temperature), or disturbance variables (such as changes in supply pressure). Both the stationary and dynamic performance are therefore unsatisfactory. These disadvantages are largely eliminated by a closed control loop, an important component of the control loop being a sensor element measuring the control variable, a pressure sensor in the present case.
It is advantageous to integrate the pressure sensor into the electrohydraulic actuator of the control loop, i.e., into the pressure regulating valve, since this reduces assembly work on the part of the customer. A system of this type is described, for example, in the European Patent No. EP 0 971 278 A1. In this patent, the pressure to be regulated is measured by a pressure sensor situated in the solenoid part and, more specifically in an armature housing, of the pressure regulating valve. For this purpose, the pressure signal present in the valve part must be guided through the armature housing. The pressure connection routed through the armature housing for this purpose corresponds in the hydraulic sense to a long duct of comparatively high geometric complexity and length and represents a hydraulic transmission link along which the measured variable pressure is filtered. As a result, both the amplitude and phase of the signal changes, which is disadvantageous insofar as the pressure signals are transmittable true to original only up to a relatively low cutoff frequency. Consequently, undesirable corruption of the measurement result may occur.